A home appliance such as an air conditioner needs to include a sensitive and simple electromagnetic wave detector which detects the position of a human body or temperature distribution in a room, in order to realize power saving operation and comfortable temperature control. As such an electromagnetic wave detector, an infrared sensor called a thermal infrared sensor or a uncooled infrared sensor is used particularly for detecting an infrared ray. The infrared sensor detects an incident infrared ray by absorbing the infrared ray, converting the infrared ray into heat, and converting the heat into an electric signal. The thermal infrared sensor uses a structure where an infrared ray-absorption unit is held in midair by a support leg and, thus, the thermal insulation property of the infrared-ray absorption unit is improved and a change in temperature of an electromagnetic wave absorption unit is read highly accurately.
For example, in a thermopile infrared sensor including a thermocouple, a hot junction of the thermocouple is provided above a cavity portion, and a cold junction of the thermocouple is provided on a frame body which surrounds the cavity portion. The temperature of the hot junction is detected from a thermoelectromotive force generated due to the difference in temperature between the hot junction and the cold junction. Sensitivity of the thermopile infrared sensor is improved, for example, by reducing thermal capacity of the hot junction, reducing thermal conductivity from the hot junction to the cold junction, and increasing absorption by an electromagnetic-wave absorbing film (for example, see Patent Document 1).